1. The Field of the Invention
The present invention relates generally towards a lung assist device that transports oxygen into and carbon dioxide out of the circulating venous blood. More particularly, the present invention is directed towards a compliant blood gas exchanger which can be used intracorporeally or extracorporeally to efficiently, effectively, and safely exchange oxygen and carbon dioxide for patients with advanced respiratory failure.
2. The Relevant Technology
Thousands of people suffer from inadequate blood gas exchange, which includes both inadequate input of oxygen and inadequate removal of carbon dioxide from the blood. Inadequate blood gas exchange can be caused by many conditions or illnesses such as pneumonia, pneumonitis, atelectasis, various heart and circulatory ailments, blood in the lungs, obstruction of pulmonary ventilation, acute respiratory distress syndrome, or lung injury caused by heat, noxious gases and other factors.
One alternative to treating advanced respiratory ailments is to opt for a lung transplant. This is expensive and risky for the patient. Hence, lung assist devices are a preferred method of treating respiratory disease. There are several types of conventional lung assist devices that supply oxygen to and remove carbon dioxide from a patient's blood for a short term. These devices can be conveniently separated into three categories: respirators, extracorporeal oxygenators and intravascular lung assist devices. In general, respirators are useful in improving the efficiency of a patient's blood gas exchange when used judiciously in low or moderate intensity. However, respirators are not suitable for use where a patient's damaged or diseased lungs require rest or are simply incapable of performing the required respiration. They are also not suitable for high-intensity blood gas exchanges (high pressure, gas flow rate, and/or concentration of oxygen).
Extracorporeal oxygenators, common referred to as heart-lung machines, usually take the form of extracorporeal membrane oxygenators (ECMOs) and are most frequently used for relatively short intervals, such as during surgery where the circulation through a patient's heart and lungs is temporarily bypassed. Extracorporeal oxygenators are generally not used for extended or long-term critical care because the machines are expensive to operate and require almost constant supervision and monitoring by skilled technicians. Conventional heart-lung machines also require systemic administration of anticoagulants, which may create additional problems such as internal bleeding, especially when systematically administered on a long-term basis.
Extracorporeal membrane oxygenators typically include a gas permeable membrane in which oxygen-rich gas flows on one side of the membrane and blood flows on the other side. As the blood flows along one side of the membrane, oxygen supplied to the other side of the membrane permeates through the membrane into the blood while carbon dioxide permeates through the membrane from the blood into the gas on the other side of the membrane. Oxygen will diffuse or travel across the membrane and enter the blood if there is a sufficient pressure gradient between the oxygen supply and the blood. In addition, carbon dioxide will diffuse from the blood, across the membrane, and into the gas chamber. The membrane separating the blood from the gas allows blood gas exchange of the blood without introducing oxygen bubbles into the blood. The gas permeable membrane is typically either a microporous membrane that allows gas to exchange through the micropores or a continuous membrane that allows gas to exchange through the membrane without the gas and blood directly interfacing.
Respirators and ECMOs, however, place more strain on the lungs, which may be diseased or injured and unable to function at full capacity. In order to allow diseased or damaged lungs to heal, it is desirable to allow the lungs to rest and then gradually increase their function. Because conventional respirators place more strain and require more work from the lungs, this often prevents the lungs from healing or recovering. Additionally, these machines are often used in late stages of respiratory failure when patients have multi-organ failure from the inadequate blood gas exchange and any additional stress to a patient could be critical.
Intravascular lung assist devices have also been developed to provide blood gas exchange in patients with respiratory failure. However, intravascular lung assist devices can provide only a portion of the blood gas exchange requirements of a patient with advanced lung failure. Furthermore, they have not been used continuously for more than six to eight weeks.
Thus, it would be an improvement in the art to have a blood gas exchanger which (1) is small enough to be portable and/or implantable; (2) is employable either extracorporeally and intracorporeally; (3) compliant enough to present high systolic blood pressure peaks when receiving blood pumped by the patient's right or left ventricle; (4) provides a physiologically compatible blood flow rate and pattern; (5) is safe and easy to use; (6) is sufficiently non-thrombogenic and biocompatible with the blood such that systemic anticoagulation during use of the blood gas exchanger is not necessary; (7) is amenable to automatic control by servo mechanisms; and (8) provides more efficient and longer term gas exchange than is currently available in the art.